1. Field of the Invention
The present invention relates to a recording apparatus for electrostatic images having therein a means for maintaining the temperature of a photoreceptor within a certain range.
2. Description of the prior art
Specific characters of a photoreceptor to be used in a recording apparatus for electrostatic images such as a charging voltage characteristic, dark voltage and others may change according to the temperature of the photoreceptor and a photosensitivity thereof also increases as the temperature of the photoreceptor rises. Accordingly, when the temperature of the photoreceptor is excessively low, the so-called grey background phenomenon wherein toner adheres to the background of the image takes place and when the temperature of the photoreceptor is excessively high, the image density is lowered, which adversely affects the quality of the recorded material.
In the recording apparatus for electrostatic images in the practical use, there exist many factors affecting the temperature of the photoreceptor such as electric parts of every kind provided in the case thereof or the heat generated from the heat roller for image-fixing and others and therefore it is important to avoid such effect. Especially in the recording apparatus for electrostatic images of the type disclosed in Japanese Patent Publication Open to Public Inspection No. 78559/1974 for example wherein toner images formed on the photoreceptor that is the subject of the present invention are contacted and transferred onto the heated intermediate transferring material and the toner in the molten state is further transferred again and fixed onto the final support such as a paper and thus the recorded materials are obtained, the temperature fluctuation on the photoreceptor tends to be great because the heated intermediate transferring substance contacts the photoreceptor directly thus the quality of the recorded material varies remarkably between the moment right after the start of the apparatus and the moment after a long waiting period or between the moment of the start of continuous recording in many sheets and the moment of the completion thereof, which sometimes causes difficulties in the practical use.
As a method to prevent the quality fluctuation on the recorded material based on the temperature fluctuation on the photoreceptor mentioned above, there have been proposed the methods to detect the change in the surface potential on the photoreceptor or the change in the electrostatic contrast on the electrostatic latent image formed on the photoreceptor depend on the temperature fluctuation and thereby automatically adjust the conditions in each step of charging, exposure and developing. However, all these methods require the addition of the detector for the voltage-measurement and complicated devices such as the computing circuit and control circuit for the automatic control for the steps of charging, exposure and developing. Further, the aforesaid adjustment for each step cannot compensate fully and it is almost impossible to obtain an image quality of a certain high grade.